Rod Group and Individual Control System - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 339

drive step, that is why for precise indication the
count of drive steps in not required. Such possibil-
ity was reached due to usage of shunt, covering 9
inductance coils of the sensor in, which magnetic
and non-magnetic segments of different length
alternate in such way, that if shunt position changes
on one step, at least one of 9 coils changes its
inductance (Nikituk, 2004). It allows to receive a
unique code combination (9 coils with separated
inputs can form 2 9 = 512 different combinations,
191 of which are used, also within working range
between upper and lower limit switch - 175 code
combinations).
Coils are placed on 100 mm distance from one
another, fastened by non-magnetic remote patches
and are embedded inside the case from magnetic
soft steel, filled by nitrogen. Coil wound is made
of heatproof wire on core of magnetically soft
steel, coil finishes are out of sensor case, through
wall tube. Coils of each sensor are supplied from
CR position cabinet of stabilized alternating cur-
rent (200 mА, 250 Hz). Usage of stepping sensor
provides a possibility to diagnosis CR drive (detect
skip of steps and slippage), and in case of fall-
ing of control rod - to determine duration of CR
passing over each section of the core.
Each of three CR position cabinets has 18
independent CR position monitoring channels,
fourth cabinet has 7 channels. Each channel:

precise CR position and sends continuous
direct current signal, which represents the
precise CR position;

• Forms and sends signals initiating drive

stop in case the control rod reached posi-
tion of lower or upper limit switch into ad-
jacent channel in power control cabinet;

• Receives signal of electromagnet CR drive

disconnecting of power supply from ad-
jacent channel in power control cabinet;
identify control rod falling (on transmis-
sion time from section 2 to lower limit
switch, if it is shorter than 4 s); switches
on light-emitting diode on the front panel;
deines CR transmission time of each core
section and general duration of falling;

• Sends to each signal forming cabinet (via

base and reserve iber-optical lines) data
on rough and precise CR, electromagnets
disconnecting of power supply, CR falling
and duration of falling.

Each CR position cabinet performs continuous
automatic monitoring over technical condition
of its component parts, CR position sensors and
communication lines (resistance and inductance
of coils, isolation resistance, absence of discon-
nection and short circuits). Diagnostic messages
on test results are sent to workstation (along with
data on CR falling duration). Generalized signal
about faults is sent to workstation via separate line.
Power control cabinets are intended for direct
control of CR drives. One cabinet has four power
control channels; each of them controls one drive,
performing the following functions:

• Sets current of a speciied form and fre-

quency required for sensor performance;
receives signals from sensor; deines rough
CR position and send direct current contin-
uous signals to indication devices in MCR
and ECR;

• Receives impulses from the adjacent chan-

nel in power control cabinet, each of them
corresponds to upwards or downwards
drive movement on one step; counts quan-
tity of steps made by the drive inside the
respective section of rod operating; deined

• Receiving of electrical signals from each

signals forming cabinet initiated by emer-
gency reactor protection and accelerated
preventive protection commands ERP or
RAPP via basic and reserve buses (see
Figure 4); logical processing of the re-